title: Effects of dietary fibre and protein on urea transport across the cecal mucosa of piglets.
abstract: In ruminants, gastrointestinal recycling of urea is acutely enhanced by fibre-rich diets that lead to high ruminal concentration of short chain fatty acids (SCFA), while high ammonia has inhibitory effects. This study attempted to clarify if urea flux to the porcine cecum is similarly regulated. Thirty-two weaned piglets were fed diets containing protein (P) of poor prececal digestibility and fibre (F) at high (H) or low levels (L) in a 2 × 2 factorial design. After slaughter, cecal content was analyzed and the cecal mucosa incubated in Ussing chambers to measure the effect of pH, SCFA and NH4 (+) on the flux rates of urea, short-circuit current (I sc) and tissue conductance (G t). NH4 (+) significantly enhanced I sc (from 0.5 ± 0.2 to 1.2 ± 0.1 μEq cm(-2) h(-1)). No acute effects of SCFA or ammonia on urea flux were observed. Tissue conductance was significantly lower in the high dietary fibre groups irrespective of the protein content. Only the HP-LF group emerged as different from all others in terms of urea flux (74 ± 6 versus 53 ± 3 nmol cm(-2) h(-1)), associated with higher cecal ammonia concentration and reduced fecal consistency. The data suggest that as in the rumen, uptake of ammonia by the cecum may involve electrogenic transport of the ionic form (NH4 (+)). In contrast to findings in the rumen, neither a high fibre diet nor acute addition of SCFA enhanced urea transport across the pig cecum. Instead, a HP-LF diet had stimulatory effects. A potential role for urea recycling in stabilizing luminal pH is discussed.
authors.affiliation: Department of Veterinary Medicine, Institute of Veterinary Physiology, Freie Universität Berlin, Oertzenweg 19b, 14163, Berlin, Germany, stumpff@zedat.fu-berlin.de.
authors.forename: F
authors.initials: F
authors.lastname: Stumpff
authors.forename: U
authors.initials: U
authors.lastname: Lodemann
authors.forename: A G
authors.initials: AG
authors.lastname: Van Kessel
authors.forename: R
authors.initials: R
authors.lastname: Pieper
authors.forename: S
authors.initials: S
authors.lastname: Klingspor
authors.forename: K
authors.initials: K
authors.lastname: Wolf
authors.forename: H
authors.initials: H
authors.lastname: Martens
authors.forename: J
authors.initials: J
authors.lastname: Zentek
authors.forename: J R
authors.initials: JR
authors.lastname: Aschenbach
mesh_terms: D000641:Ammonia / Q000378:metabolism; D000704:Analysis of Variance; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002432:Cecum / Q000166:cytology* / Q000378:metabolism; D002849:Chromatography, Gas; D004043:Dietary Fiber / Q000494:pharmacology*; D004044:Dietary Proteins / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D034421:Sus scrofa / Q000378:metabolism*; D014508:Urea / Q000378:metabolism*
chemical_list: D004043:Dietary Fiber; D004044:Dietary Proteins; D000641:Ammonia; D014508:Urea